Broach



Aug. 23, 1966 J. A. PSENKA 3,267,552

BROACH Original Filed April 10, 1961 2 Sheets-Sheet 1 FIGJ.

INVENTOR.

JOSEPH APSENKA J/LAATTORNEYS 3, 1966 J. A. PSENKA 3,267,552

BROACH Original Filed April 10. 1961 3 Sheets-Sheet 2 INVENTOR.

JOSEPH A. PSENKA W l I /r z ww United States Patent 3,267,552 BROACH Joseph A. Psenka, Bloomfield Hiils, Mich, assignor to National Breach & Machine Company, Detroit, Mich, a corporation of Michigan Original application Apr. 10, 1961, Ser. No. 101,887. Divided and this application Oct. 19, 1964, Ser. No. 404,632

Claims. (Cl. 29-951) The present invention relates to a broach and is a division of my copending application, U.S. Serial No. 101,887, filed April 10, 1961, now Patent No. 3,178,800. More particularly thi invention relates to a broach comprising a plurality of sections, a leading one which is a roughing section adapted to rough out the teeth of a gear or splined element, and a following one in the form of a finishing section adapted to finish the teeth of the workpiece with extreme accuracy.

Breaches of the type described have been utilized in the industry. However, certain problems have been encountered. One 'of the main problems is that the side of the part which is produced by the obtuse side of the broach ha more stock removed from it than from the side of the part which is produced by the acute side of the broach. This usually results in the acute side not cleaning up fully so that the errors of form introduced into the part by the roughing section of the broach are not entirely corrected or eliminated by the side shaving shell forming the finishing section of the broach.

The present invention relates primarily to means for correcting errors of form in the broach part which are introduced into the part by the roughing section of the broach. This is accomplished by providing an improved broach or a side shaving shell which is adapted to be mounted at the rear of the roughing section of the broach so as to completely remove the aforesaid errors.

It is an object of the present invention to provide a full form finishing broach of the chanacter described in which the finishing section is connected to the leading roughing section in such a manner that the finishing section will locate itself accurately in the workpiece and will therefore produce teeth on the workpiece which, for practical purposes, have the same accuracy as the teeth on the finishing section of the broach.

Another object of the present invention is to provide a broach having a finishing section wherein the leads on the obtuse and acute sides of the teeth are decreased from the true lead so that the obtuse side produces a counter force to the natural rotative force that the acute side produces to pull the part into the obtuse side, thereby balancing stock removal from the broach part.

Still another object of the present invention is to provide a broach having a series of longitudinally spaced finish cutting teeth arranged on a center line which is adapted to traverse a lead path divergent from the path which the broach traverses.

A further object of the present invention is to provide a broach assembly having a leading broach section provided with longitudinally aligned series of progressively stepped roughing teeth arranged in circumferentially aligned groups, with the teeth in each of the series arranged on a center line, a finishing section having longitudinally aligned series of finishing teeth arranged in circumferentially aligned groups, with the finishing teeth of each series arranged in such a manner as to have the center line thereof offset from the corresponding center line in the leading broach section so that the center line of the finishing teeth is adapted to traverse a lead path divergent from the path which the broach traverses, and means for interconnecting the sections so as to maintain the aforesaid offset center line relationship.

It is thus another object of this invention to provide a simplified low cost structure of the aforementioned type having certain advantages contributing to efliciency, reliability and long life as well as ease of maintenance.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating preferred embodiments of the invention, wherein:

FIGURE 1 is a side elevation of the broach assembly.

FIGURE 2 is a side elevation of the leading roughing section of the broach.

FIGURE 3 is an end view of the leading section of the broach seen from the right in FIGURE 2.

FIGURE 4 is an enlarged view of adjacent teeth illustrated in FIGURE 1 taken on the line 4--4 thereof.

FIGURE 5 is an enlarged view of adjacent teeth illustrated in FIGURE 1 taken on the line 5-5 thereof.

FIGURE 6 is a side elevation of the novel side shaving shell.

FIGURE 7 is an end view of the side shaving shell shown in FIGURE 6.

FIGURE 8 is a view of adjacent teeth of the side shaving shell looking in the direction of line 88 of FIGURE 6.

FIGURE 9 is a diagrammatic representation illustr-ating the deviation of the leads on the acute and obtuse sides from the true lead center line of the side shaving shell.

In the broaching of internally toothed members, such as internal gears, spline members or the like, it is possible to produce broaching elements having substantially any required degree of accuracy. However, in. use, such a broaching element can reproduce itself with substantially perfect accuracy only when it is not subject to negative factors occasioned by an earlier stage of the broaching operation. The present invention relates to a broach Which has a roughing section and a finishing section, with the finishing section taking the form of a replaceable side shaving shell which is affixed to and located on the rear end of the broach body following the roughing section, such as disclosed in my Patent 2,987,801 which issued on June 13, 1961. Certain aspects of the invention may be embodied in a finishing broach construction whether formed as a part of a broach including the finishing construction or formed as a separate broach.

Referring now to the drawings, the leading section of the broach assembly 10 is shown in FIGURES 1 and 2 and is designated by the numeral 11 and comprises a head 12 adapted to be connected to a suitable device for pulling the broach through a hole in a workpiece. Conveniently, the roughing section of the broach is indicated generally at 14 and includes a series of continuous interrupted annular blades or ribs 16 adapted to form separate cutting teeth 20. The rear part of the roughing section includes alternate round and spline teeth. The round teeth or blades 18 are adapted to machine the hole in the workpiece to true cylindrical formation. The spline cutting teeth 20 are progressively stepped from front to rear and are backed off on the top at an angle phi and the sides thereof are relieved to within inch to inch of the top of the profile. The round teeth 18 are also backed olf at an angle alpha.

It will be appreciated that the cutting teeth 20 are arranged in axial alignment if the broach 1'0 is for the purpose of producing spur teeth, or in helical alignment if the broach is for the purpose of producing helical teeth. The term longitudinal alignment or the like is intended to cover arrangements for producing both spur and helical gears.

At the following end of the roughing section 14 of the broach assembly is a cylindrical support 22 having a reduced portion 24 which forms a shoulder 26. Rearwardly of the reduced portion 24 a support portion 22 is threaded as indicated at 28. Rearwardly of the threaded portion 28 is provided a cylindrical support portion 3f).

Directly to the rear of the final blade of the roughing section 14 there is a cylindrical surface 32, the opposite sides of which are machined away as indicated to form rearwardly facing flat abutment surfaces 34 and radially outwardly facing flat surfaces 36. This arrangement provides a fiat transversely extending key 38. As shown in FIGURE 1, the following finishing broach section or side shaving shell 40 is assembled on the support portion 22 of the leading section 11. Rearwardly of the finishing section or shell 40 is located a spacer 41 followed by a round shell 42 comprising a plurality of continuous round uninterrupted blades or ribs 44. The finishing shell 40, spacer 41 and side shaving shell 42 are retained on the support portion 22 of the leading section 11 in assembled relation by nut 48 threaded to the threaded portion 28 of the leading broach section 11.

The finishing section or shell 40 is essentially tubular in shape having toothed cutting blades 50 forming longitudinally aligned series of cutting teeth 52. Again, the cutting teeth extend in axially disposed series if the broach 10 is to form a spur member and the series are helically aligned if the broach 10 is used to produce helical teeth on the workpiece. At the leading end of the finishing section 40, a notch or keyway is provided which extends diametrically across the leading end thereof and is dimensioned to receive the key 38 at the following end of the roughing section of the broach. The finishing section 40 is generally provided with a central opening, the intermediate portion of which is enlarged to provide clearance and the ends of which are of slightly reduced size to provide guide surfaces which are guidingly received on the cylindrical surface of the support portion 22 of the leading section 11 of the broach 10.

It will 'be observed in FIGURE 1 that the nut 48 has the front portion or forwaard end thereof engageable with the rear end of the round shell 42 so as to urge the spacer 41 into engagement with the shoulder 26. With such a key and keyway construction between the roughing and finishing sections a small clearance in the amount of .002 inch is sufficient to permit limited circumferential relative movement between the roughing and finishing broach sections. In addition, the key and keyway constructions of the sections are properly related with respect to the cutting teeth thereon so that the cutting teeth 52 on the finishing section are in substantial true alignment with the teeth 20 of the roughing section. Nevertheless, as the finishing section 40 moves into action, it is permitted to float so that it aligns itself with substantial perfect accuracy with respect to the teeth as partially roughed out by the roughing section of the broach. The teeth 52 of the finishing section 40 are of less height than those of the roughing section and hence, out only on the sides. The top portions of the teeth 52 are thus able to pass in clearance through the grooves or slots provided at the bottom of the tooth spaces cut by the roughing section. The widths of the side shaving teeth increase from front to rear. The broach assembly just described is disclosed in the aforesaid Patent 2,987,801.

Certain problems have been encountered with the use of side shaving shells 40 of the type just described in that the side of the part which is produced by the obtuse side of the broach has more stock removed from it than from the side of the part which is produced by the acute side of the broach. This results sometimes in the acute side not cleaning up entirely so that the errors of form introduced into the broach part by the roughing section are not eliminated by the side shaving shell in a practical length of shell.

FIGURE 6 shows a novel side shaving shell which is represented by the numeral 54. The shell 54 has a series of longitudinally aligned helical teeth 56. In the past, the teeth 56 have followed a true lead center line as is diagrammatically represented by the line 58. With this type of prior art construction, the obtuse sides of the teeth were on a true lead as is diagrammatically represented by the line 60. Also, the acute sides of the teeth were also on a true lead as represented by the line 62. However, with such a construction, it was found that the obtuse side of the teeth 56 removed more stock from the part on circular tooth thickness than the acute side. In order to correct the errors, it was found that it was desirable to change the leads on the teeth from true leads as just described so as to actually produce a counter force to the natural rotative force that the acute side is producing. This is accomplished by decreasing the lead on the obtuse and acute sides of the teeth. In other words, the helix angle on the acute and obtuse sides is increased. However, the total amount of stock removal is the same as if true leads are actually present. By incorporating the changes in the leads, the obtuse side presents a counter force that balances out the natural tendency of the acute side to pull the part into the obtuse side. Described in another manner, the center line of the tooth is adapted to move at a different lead than the broach itself is moving or turning.

The acute side which represents an off lead condition is represented by the numeral 64, while the off lead condition in the obtuse side is represented by the numeral 66. With such a construction, the amount of off lead of the obtuse side is greater than the amount of off lead on the acute side and is shown in FIGURE 6 by the relationship of X to Y in which X is greater than Y.

With the present invention, the lead on the obtuse side and acute side would be shorter than that caused by the normal cut per tooth. The center line of the teeth would be on a shorter lead. FIGURE 9 diagrammatically illustrates the longitudinally aligned first and last teeth on the shell represented by the numerals 68 and 70 respectively. When the teeth are on the true lead center line 58, X equals Y However, when the teeth are not symmetrical about a true lead center line, X is greater than Y as previously described. In each case shown, X plus Y equals Z and X plus Y equals Z where Z is the total stock removal. This embodiment provides a broach having finishing teeth in which the center line of the finishing teeth traverses a lead path divergent from the path which the broach proper is traversing.

The drawings and the foregoing specification constitute a description of the improved broach in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What I claim as my invention is:

l. A broach comprising a series of longitudinally spaced finish cutting teeth arranged on a center line which is adapted to traverse a lead path divergent from the path which the broach traverses.

2. A broach comprising a series of longitudinally spaced finish cutting teeth disposed in aligned spiral relation, the teeth having a center line disposed in a spiral slightly offset from a true lead angle in such a manner that the center line is adapted to traverse a lead path divergent from the path which the broach traverses.

3. A broach comprising a series of longitudinally spaced finish cutting teeth of progressively increasing width disposed in aligned spiral relation, the teeth having a center line disposed in a spiral slightly offset from a true lead angle in such a manner that the center line is adapted to traverse a lead path divergent from the path which the broach traverses.

4. A broach comprising a leading roughing section having longitudinally aligned stepped rough cutting teeth arranged on a center line and a following finishing section having accurately formed longitudinally aligned finish cutting teeth arranged on a center line which is adapted to traverse a lead path divergent from the path which the broach traverses.

5. A broach comprising a leading roughing section having longitudinally aligned stepped rough cutting teeth arranged on a center line and a following finishing section having accurately formed longitudinally aligned finish cutting teeth of progressively increasing width arranged in such a manner as to have the center line thereof offset from the center line of the rough cutting teeth in the roughing section,

6. A broach assembly comprising a leading broach section provided with longitudinally aligned series of progressively stepped roughing teeth arranged in circumferentially aligned groups, with the teeth in each of the series arranged on a center line, a finishing section having longitudinally aligned series of finishing teeth arranged in circumferentially aligned groups, with the finishing teeth of each series arranged in such a manner as to have the center line thereof offset from the corresponding center line in the leading broach section so that the center line of the finishing teeth is adapted to traverse a lead path divergent from the path which the broach traverses, and means for interconnecting the sections so as to maintain the aforesaid offset center line relationship.

7. A broach assembly defined in claim 6 wherein said finish cutting teeth are arranged in progressively increasing width and height.

8. A broach assembly defined in claim 6 wherein the teeth of said leading broach section are of equal width.

9. A broach assembly comprising a leading section having longitudinally aligned series of progressively stepped cutting teeth, and a support portion following said cutting teeth having a cylindrical support surface, a finishing broach shell having longitudinally aligned series of finishing teeth arranged in circumferentially aligned groups, said shell having a cylindrical guide surface engageable with the cylindrical support surface of said leading section, the finishing teeth of each series arranged in such a manner as to have the center line thereof offset from the corresponding center line of the teeth in the leading section so that the center line of the finishing teeth is adapted to traverse a lead path divergent from the path which the broach traverses, and means for retaining said shell on said support portion to maintain the aforesaid offset center line relationship.

10. An internal broach comprising a tubular body having on the inner periphery thereof a series of longitudinally spaced finish cutting teeth of progressively increasing width arranged on a center line which is adapted to traverse a lead path divergent from the path which the broach traverses.

No references cited.

WILLIAM W. DYER, IR., Primary Examiner.

H. L. HINSON, Assistant Examiner. 

2. A BROACH COMPRISING A SERIES OF LONGITUDINALLY SPACED FINISH CUTTING TEETH DISPOSED IN ALIGNED SPIRAL RELATION, THE TEETH HAVING A CENTER LINE DISPOSED IN A SPIRAL SLIGHTLY OFFSET FROM A TRUE LEAD ANGLE IN SUCH A MANNER THAT THE CENTER LINE IS ADAPTED TO TRAVERSE A LEAD PATH DIVERGENT FROM THE PATH WHICH THE BROACH TRANVERSE. 